Liquid crystal display device and method for manufacturing the same

ABSTRACT

A liquid crystal display device employs a white sub-pixel among RGBW-4 sub-pixels as a view control component to realize a narrow viewing angle or a wide viewing angle in a fringe field switching mode. The LCD device comprises gate lines and data lines crossing each other to define RGBW sub-pixels on a first substrate, a thin film transistor formed at each crossing of the gate and data lines; a first common electrode in each region of the RGBW sub-pixels, a pixel electrode connected to the thin film transistor and insulated from the first common electrode, the pixel electrode having at least one slit, a second substrate attached to the first substrate, wherein the first and second substrate face each other with a liquid crystal layer interposed therebetween, and a second common electrode on the second substrate and corresponding to each W sub-pixel.

This application claims the benefit of Korean Patent Application No.10-2005-0131564, filed on Dec. 28, 2005, which is hereby incorporated byreference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) device,and a method for manufacturing the same. More particularly, the presentinvention relates to a liquid crystal display device that employs awhite sub-pixel among RGBW-4 sub-pixels as a view control component torealize a narrow viewing angle as well as a wide viewing angle in afringe field switching mode, and a method for manufacturing the same.

2. Discussion of the Related Art

In recent years, rapid advances in the performance of an active matrixliquid crystal display (“LCD”) device have resulted in variousapplications of the LCD device, such as screens for flat panel TVs, andmonitors for portable computers.

Among the active matrix LCD devices, a twisted nematic (TN) type LCDdevice is widely used. The TN type LCD device refers to an LCD devicewherein, with liquid crystals arranged to have liquid crystal directortwisted 90 degrees between two substrates, each having an electrode, theliquid crystal director is driven via application of a voltage to theelectrodes.

Although the TN type LCD device has been spotlighted in terms of itsexcellent contrast and color reproducibility, it suffers from asignificant problem in that it has a narrow viewing angle.

In order to solve the problem of the TN type LCD device having thenarrow viewing angle, a fringe field switching (“FFS”) mode type LCDdevice has been introduced, wherein a counter electrode and a pixelelectrode are formed of a transparent conductor, and are spaced apart bya narrow distance to allow liquid crystal molecules to be operated by afringe field created between the counter electrode and the pixelelectrode.

The FFS mode type LCD device will be described in detail hereinafter.

FIG. 1 is a plan view illustrating a related art FFS mode type liquidcrystal display device, and FIG. 2 is a cross-sectional view taken alongline I-I′ of FIG. 1.

In FIGS. 1 and 2, the related art FFS mode type LCD device comprises aTFT array substrate 11, which is formed thereon with gate lines 12 anddata lines 15, formed of metal, crossing each other to definesub-pixels, a common line 25 disposed in parallel to the gate line 12, athin film transistor formed at each crossing portion of the gate anddata lines to act as a switching element to switch a voltage on/off, anda counter electrode 24 and a pixel electrode 17 formed of a transparentmetal in each sub-pixel while being isolated from each other via adielectric layer so as to overlap with each other; Here, the counterelectrode 24 is brought into contact with the common line 25.

More specifically, the counter electrode 24 is formed in a plate shapewithin each sub-pixel, and the pixel electrode 17 is divided into pluralsub-pixel electrodes in a direction of the data lines to define slits 60between the sub-pixel electrodes. Here, when a V_(com) signal is appliedto the counter electrode 24, and a pixel signal is applied to the pixelelectrode 17 through the thin film transistor, a fringe field isgenerated between the counter electrode 24 and the pixel electrode 17.

Each of the slits 60 has a width of about 2-6 gm, and liquid crystalsare driven by the fringe field generated between the counter electrode24 and the pixel electrode 17. In other words, when voltage is notapplied, the liquid crystals are rotated from an initial orientation bythe fringe field E via rubbing, and allow light to be transmittedtherethrough.

Meanwhile, a color filter array substrate 21 is assembled opposite theTFT array substrate 11 with a liquid crystal layer 31 interposedtherebetween, in which the color filter array substrate 21 comprisesRGB-color filter layers 23 arranged in a predetermined pattern torealize red, green and blue colors, and black matrices 22 to partitionthe RGB-color filter layers from each other while shielding light.

The color filter layers 23 are formed such that respective sub-pixelshave their own single pigment and are independently driven to exhibitcolor of one pixel via combination thereof.

The RGB-color filter layers 23 in the LCD device can be arranged in astripe type, a mosaic type, a delta type, a quad type, and the likeaccording to an arranging manner of the layers, and can be arranged invarious arrays according to the size of a liquid crystal display panel,shape of the color filter, and color arrangement.

Such a related art liquid crystal display device has problems asfollows.

For the related art FFS mode type LCD device, it is necessary to enableeasy conversion between a narrow viewing angle and a wide viewing anglein order to prevent private information of an user from being seen byother persons near the user. To this end, a view control layer can beadditionally formed in the device, or a view control electrode can beadditionally formed on the overall upper plate to control the viewingangle. However, these techniques have some problems as follows. First,the view control effect is insignificant. Secondly, enlargement in therange of the electrode structure modified or added to increase the viewcontrol effect is very disadvantageous in view of an aperture ratio.Thirdly, a front contrast ratio (CR) can also be significantly reducedupon the narrow viewing angle.

The most important problem of these techniques is in a complicateddriving method due to insertion of the additional electrode layer andapplication of signals.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay device and a method for manufacturing the same thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An advantage of the present invention is to provide a liquid crystaldisplay device that can realize a narrow viewing angle in addition to awide viewing angle in a fringe field switching (FFS) mode in such a wayof allowing a white sub-pixel among RGBW-4 sub-pixels to be driven inthe same FFS mode as that of the adjacent RGB sub-pixels for the wideviewing angle while being driven to form a vertical electric fielddifferent from that of the adjacent RGB sub-pixels only for the narrowviewing angle, and a method for manufacturing the same.

Additional advantages and features of the invention will be set forth inpart in the description which follows and in part will become apparentfrom the descriptions or may be learned by practice of the invention.These and other advantages of the invention may be realized and attainedby the structure particularly pointed out in the written description andclaims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, there isprovided a liquid crystal display device, comprising: gate lines anddata lines crossing each other to define RGBW sub-pixels on a firstsubstrate; a thin film transistor formed at each crossing of the gateand data lines; a first common electrode formed in each region of theRGBW sub-pixels; a pixel electrode connected to the thin film transistorand insulated from the first common electrode, the pixel electrodehaving at least one slit attached to the first substrate, wherein thefirst and second substrates face each other with a liquid crystal layerinterposed therebetween; and a second common electrode formed on thesecond substrate and corresponding to each W sub-pixel.

In accordance with another aspect of the present invention, there isprovided a method for manufacturing a liquid crystal display device,comprising: forming first common electrodes on a first substrate;forming gate lines and data lines to cross each other to define RGBWsub-pixels on the first substrate; forming a thin film transistor ateach crossing of the gate and data lines; forming a passivation layer onan overall surface of the first substrate including the thin filmtransistor; forming pixel electrodes on the passivation layer, eachhaving at least one slit; attaching a second substrate to the firstsubstrate, wherein the first substrate and second substrate face eachother, the second substrate having a second common electrode formed tocorrespond only to each W sub-pixel; and forming a liquid crystal layerbetween the first and second substrates.

In this manner, the present invention is characterized in that the wideand narrow viewing angles are controlled by means of the white sub-pixelamong the RGBS-4 sub-pixels, in which, with the second common electrodeintroduced only into each W sub-pixel on the second substrate (a colorfilter array substrate), a voltage is applied in such a way that, forthe case of wide viewing angle, the second common electrode of thesecond substrate is supplied with the same level of voltage as that ofthe first common electrode of the first substrate (thin film transistorarray substrate) or is not supplied with any voltage to make it in afloating state, and in the case of narrow viewing angle, an electricfield difference of about 1˜4 V or about −4˜−1 V is induced between thesecond common electrode of the second substrate and the first commonelectrode of the first substrate.

That is, in the LCD device in which one pixel is constituted by RGBWfour sub-pixels, the RGB sub-pixels are always driven in the FES mode,whereas the W sub-pixel is driven in the FFS mode for the wide viewingangle, thereby increasing a viewing angle, and generates the verticalelectric field for the narrow viewing angle, thereby reducing theviewing angle.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a plan view illustrating a related art FFS mode type liquidcrystal display device;

FIG. 2 is a cross-sectional view taken along line I-I′ of FIG. 1;

FIG. 3 is a plan view illustrating an FFS mode type liquid crystaldisplay device in accordance with the present invention;

FIG. 4 is a cross-sectional view taken along line II-II′ of FIG. 3;

FIG. 5 is a view illustrating patterns on a color filter array substratein accordance with the present invention;

FIGS. 6A and 6B are cross-sectional views illustrating a mode for a wideviewing angle of the LCD device in accordance with the presentinvention;

FIGS. 7A and 7B are cross-sectional views illustrating a mode for anarrow viewing angle of the LCD device in accordance with the presentinvention; and

FIGS. 8A to 8D are cross-sectional views illustrating manufacturingsteps taken along lines III-III′ of FIG. 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 3 is a plan view illustrating an FFS mode type LCD device accordingto the present invention, FIG. 4 is a cross-sectional view taken alongline II-II′ of FIG. 3, and FIG. 5 is a view illustrating patterns on acolor filter array substrate according to the present invention.

In addition, FIGS. 6A and 6B are cross-sectional views illustrating amode for a wide viewing angle of the LCD device according to the presentinvention, FIGS. 7A and 7B are cross-sectional views illustrating a modefor a narrow viewing angle of the LCD device according to the presentinvention, and FIGS. 8A to 8D are cross-sectional views illustratingmanufacturing steps taken along lines III-III′ of FIG. 3.

In FIGS. 3 and 4, the LCD device according to the invention isconstituted by a TFT array substrate 111 and a color filter arraysubstrate 121 assembled to face each other with a liquid crystal layer131 interposed therebetween. The TFT array substrate 111 is formed witha thin film transistor formed in each of RGBW sub-pixels to act as aswitching element, and with first common electrodes 124 and pixelelectrodes 117 to form a fringe field. The color filter array substrate121 is formed with a second common electrode 126 only for each Wsub-pixel to control a viewing angle.

In other words, the RGB sub-pixels are adapted to allow fringe field tobe generated therein, and are driven in the FFS mode irrespective of thewide viewing angle or the narrow viewing angle, and each W sub-pixelserves as a viewing angle control sub-pixel which can control the wideviewing angle and the narrow viewing angle. For the case of wide viewingangle mode, each W sub-pixel is driven in the same FFS mode as that ofthe RGB sub-pixels, thereby increasing the viewing angle, and for thecase of narrow viewing angle mode, a vertical electric field isgenerated in each W sub-pixel, thereby reducing the contrast ratio andthe viewing angle.

Here, according to an arranging manner of the RGBW sub-pixels, the LCDdevice can be classified into a quad type LCD device wherein the RGBWsub-pixels are arranged in a square shape to form one pixel withsub-pixels of a 2×2 structure, and a stripe type LCD device wherein theRGBW sub-pixels are sequentially arranged to form one pixel with foursub-pixels.

More specifically, on the TFT array substrate 111, the RGBW sub-pixelsare defined by gate lines 112 and data lines 115 insulated from eachother via a gate insulation film 113 while vertically crossing eachother to define a thin film transistor at each crossing portion thereof.Each sub-pixel is formed therein with the first plate-shaped commonelectrode 124 formed and to which a _(Voom) signal is applied, and apixel electrode 117 having a plurality of slits 160 insulated from thefirst common electrode 124 and brought into contact with a drainelectrode 115 b of the thin film transistor such that a pixel signal isapplied to the pixel electrode 117. A fringe field is created betweenthe first common electrode and the pixel electrode via the slits 160,and drives the liquid crystal layer 131.

The first common electrodes 124 and the pixel electrodes 117 are formedby depositing and patterning a transparent conductive material such asITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide). Here, the firstcommon electrodes 124 may be formed under the gate lines or on the datalines. If the first common electrodes 124 are formed on the data lines,they are formed to be insulated from the pixel electrodes via theinsulation film.

The slits 160 of each pixel electrode are formed such that alongitudinal axis thereof is disposed in a direction of the gate linesor the data lines. The slits 160 of the pixel electrode can be disposedin the direction of the data lines in order to narrow a right and leftviewing angle. In this regard, it is necessary to dispose the slits ofthe pixel electrode in the same direction with respect to all the RGBWsub-pixels.

Each of the first common electrodes 124 is brought into contact with afirst common line 125 to receive the Vcom signal, in which the firstcommon line 125 is formed in parallel to the gate lines to receive theVc_(o)m signal from a region outside an active region.

Each of the pixel electrodes 117 is brought into contact with the drainelectrode 115 b of the thin film transistor through the passivationlayer 116, and receives the pixel signal.

Meanwhile, each of thin film transistors serves as a switching elementto control the on/off of a voltage. Each thin film transistor comprisesa gate electrode 112 a branched from an associated gate line 112, thegate insulation film 113 formed over the whole surface including thegate lines 112, a semiconductor layer 114 formed by depositingnoncrystalline silicon (a-Si) on the gate insulation film above the gateelectrode, and source/drain electrodes 115 a and 115 b branched from anassociated data line 115 while being formed on the semiconductor layerin order to serve as the switching element for controlling on/off of thevoltage.

The TFT array substrate 111 is attached to the color filter arraysubstrate 121 so as to face each other with the liquid crystal layer 131interposed therebetween. The color filter array substrate 121 comprisesblack matrices 122 partitioning the R, G and B layers from each otherwhile shielding light, color filter layers 123 of red, green, blue andwhite arranged in a predetermined pattern to realize red, green, blueand white, and a second common electrode 126 only for each of the Wsub-pixels to control a viewing angle of the W sub-pixel. The secondcommon electrode 126 is formed in a plate shape of a transparentmaterial, and formed to correspond only to each W sub-pixel.

Here, it is necessary for the second common electrode 126 to receive adifferent V_(com) signal than that of the first common electrode 124 onthe TFT array substrate. To this end, as shown in FIG. 5, a secondcommon line 127 is further added to integrally connect the second commonelectrodes 126 corresponding to the W sub-pixels with each other. Thesecond common line 127 is extended to a region outside the activeregion. The second common line 127 is formed along an edge of the pixelregion so as not to shield a region where an image is displayed, and canbe formed in parallel to the gate lines. In order to apply the V_(com)signal to the second common line 127, the second common line 127 must beconnected with an external driving circuit of the first substrate.Connection between the second common line 127 and the first substrate isvia silver dots 191, which are disposed at corners of a panel, andelectrically connect the upper and lower substrates.

Meanwhile, RGBW colors constituting the color filter layers areindependently driven to exhibit color of one pixel via combinationthereof. Here, each W sub-pixel realizes W color without forming aresist as the W color filter layer. Alternatively, the W color filterlayer of W sub-pixel is formed using a resist, which is not mixed withpigments of RGB, along with the RGB sub-pixels in a process of formingthe RGB-color filter layers.

If the process of forming the color filter layers is not performed tothe W sub-pixels, each of the W sub-pixels has a different step fromthat of the RGB sub-pixels. In this regard, an overcoat layer 128 isevenly formed on an entire surface including the color filter layers tosolve the problem of a non-uniform step over the substrate. At thistime, the second common electrode 126 is formed on the overcoat layer128 of each W sub-pixel.

As such, the LCD device according to the present invention comprises theW sub-pixels for a white pattern, which do not comprise pigment, as wellas the RGB sub-pixels so as to constitute one pixel with the RGBWsub-pixels. Here, the color filter layers are formed such that the RGBsub-pixels contain the pigments, thereby lowering the transmittance, andthe W sub-pixel does not contain the pigment, enhancing thetransmittance of the whole pixel.

Meanwhile, the LCD device further comprises an orientation filmrespectively formed on the inner surfaces of the TFT array substrate andthe color filter array substrate to arrange liquid crystal molecules ina desired direction at an initial state, and upper and lowerpolarization plates respectively attached to the outer surfaces of thecolor filter array substrate and the TFT array substrate to polarizelight. The lower polarization plate is attached to the outer surface ofthe TFT array substrate, and the upper polarization plate is attached tothe outer surface of the color filter array substrate such that apolarization axis of the lower polarization plate is orthogonal to thatof the upper polarization plate, with the orientation film disposedsubstantially parallel to the polarization axis of one of the upper andlower polarization plates.

In the drawings, the orientation film provided inside the TFT arraysubstrate is disposed substantially parallel to the polarization axis ofthe upper polarization plate, so that the liquid crystals are arrangedat an initial state in the longitudinal direction of the slits of thepixel electrode.

The LCD device according to the present invention is characterized inthat the RGB sub-pixels exhibit the same transmittance via applicationof the same voltage (FFS mode driving voltage) thereto irrespective ofthe wide viewing angle and the narrow viewing angle, and the Wsub-pixels control the viewing angle via application of differentvoltages for the wide viewing angle and the narrow viewing angle,respectively.

First, when driving the LCD device in a wide viewing angle mode, all theRGBW sub-pixels are driven in the FFS mode. In this regard, as shown inFIG. 6A, when no voltage is applied to the first common electrode 124and the pixel electrode 117, liquid crystal molecules 131 a maintain aninitial arrangement state so that incident light entering through thepolarization axis of the lower polarization plate orthogonal to aninitial arrangement direction of the liquid crystal molecules does notpass through the liquid crystal layer 131, thereby realizing a blackstate.

Next, as shown in FIG. 6B, if a Vc_(om) voltage is applied to the firstcommon electrode 124 and a pixel voltage is applied to the pixelelectrode 117, a fringe field is formed between the first commonelectrode 124 and the pixel electrode 117 so that the liquid crystalmolecules 131 a move in the horizontal direction by the fringe field.Accordingly, light entering through the polarization axis of the lowerpolarization plate passes through the polarization axis of the upperpolarization plate via the liquid crystal layer, thereby realizing awhite state.

At this time, in order to prevent the second common electrode 126 ofeach W sub-pixel from participating in formation of the fringe field, itis necessary to make the second common electrode 126 have a floatingstate wherein no voltage is applied thereto, or to apply the samevoltage as that of the first common electrode 124 thereto, therebysubstantially preventing the vertical electric field from being createdin the second common electrode.

In this manner, when the LCD device is driven in the mode for the wideviewing angle, the W sub-pixel is also operated in the FFS mode togetherwith the RGB sub-pixels, thereby satisfying compensation effect forwhite brightness while realizing the wide viewing angle.

When driving the LCD device in a narrow viewing angle mode, the RGBsub-pixels are operated in the FFS mode, whereas the W sub-pixel simplyserves to control the viewing angle and does not serve as a brightnesscompensation pixel. In this case, unlike the case of the wide viewingangle mode, the second common electrode 126 participates in formation ofthe electric field.

First, as shown in FIG. 7A, when a predetermined voltage is applied tothe second common electrode 126 of each W sub-pixel to form the verticalelectric field between the second common electrode 126 and the firstcommon electrode 124 of the W sub-pixel without applying any voltage tothe pixel electrode 117 and the first common electrode 124 of the RGBsub-pixels, liquid crystal molecules 131 a in the RGB sub-pixelsmaintain the initial arrangement state so that incident light enteringthrough the polarization axis of the lower polarization plate orthogonalto the initial arrangement direction of the liquid crystal moleculesdoes not pass through the liquid crystal layer 131, thereby realizingthe black state.

In addition, the liquid crystal molecules 131 a in the W sub-pixel aretilted in the vertical direction by the vertical electric field formedbetween the first common electrode 124 and the second common electrode126 so that light cannot be observed therethrough. In other words, lightis not observed in front of the W sub-pixel irrespective of the whitestate or the black state, there occurs light leakage in right and leftviewing angles of the W sub-pixel. That is, since the vertical electricfield is formed only in the W sub-pixel and there occurs light leakagein right and left viewing angles, the narrow viewing angle is realizedin the black state.

In conclusion, it is possible to observe a great amount of light leakedin the directions of the right and left viewing angles in the blackstate. In view of the fact that four sub-pixels constitute one pixel,when a user observes the panel in directions of the right and leftviewing angles, black brightness is rapidly increased, causing thecontrast ratio to decrease. Thus, the viewing angle of the device becomenarrow.

Meanwhile, if the V_(com) voltage is applied to the first commonelectrode 124 of the RGB sub-pixels, and a pixel voltage is applied tothe pixel electrode 117 thereof while applying a predetermined voltageto the second common electrode 126 of the W sub-pixel so as to form thevertical electric field between the second common electrode 126 and thefirst common electrode 124, the fringe field is formed between the firstcommon electrode 124 and the pixel electrode 117 of the RGB sub-pixels,as shown in FIG. 7B.

Therefore, the liquid crystal molecules 131 a in the RGB sub-pixels movein the horizontal direction by the fringe field. Accordingly, lightentering through the polarization axis of the lower polarization platepasses through the liquid crystal layer 131, thereby realizing the whitestate. In addition, the liquid crystal molecules 131 a in the Wsub-pixel are tilted in the vertical direction by the vertical electricfield formed between the first common electrode 124 and the secondcommon electrode 126, and prevent light from passing therethrough. Inthis case, although light is not observed in front of the W sub-pixel,there also occurs light leakage in the directions of the right and leftviewing angles from the W sub-pixel, thereby reducing the viewing angle.That is, the narrow viewing angle is realized in the white state byforming a horizontal electric field for the RGB sub-pixels while formingthe vertical electric field for the W sub-pixel.

At this time, in order to realize the narrow viewing angle, the pixelelectrode 117 of the W sub-pixel is supplied with a pixel voltage thesame as the V_(com) voltage applied to the first common electrode 124 orless than a threshold voltage. In addition, the first common electrode124 is supplied with the same voltage as that in the wide viewing anglemode, and the second common electrode 126 is supplied with a voltagesuch that an electric field difference of about 1-4 V or about −4-−1 Vis induced between the second common electrode 126 and the first commonelectrode 124. The voltage applied to the second common electrode 126may be either DC or AC voltage.

In this manner, in the LCD device according to the present invention,when realizing the wide viewing angle, all the RGBW sub-pixels areoperated in the FFS mode. On the contrary, when realizing the narrowviewing angle, the RGB sub-pixels are operated in the FFS mode, and theW sub-pixel is operated to form the vertical electric field between thefirst and second substrates so that the liquid crystal molecules thereinare tilted instead of being twisted, thereby preventing light from beingtransmitted through the W sub-pixel.

A method for manufacturing a liquid crystal display device will bedescribed in detail as follows.

First, in FIG. 8A, a transparent conductive material such as ITO (IndiumTin Oxide) or IZO (Indium Zinc Oxide) is deposited on a dielectricsubstrate 111, and patterned to remain in W sub-pixels, thereby formingfirst plate-shaped common electrodes 124.

Then, gate lines 112 (see FIG. 3), gate electrodes 112 a, and firstcommon lines 125 (see FIG. 3) are formed by depositing metal having alow specific resistance, such as copper (Cu), aluminum (AL), aluminumalloy (AlNd), molybdenum (Mo), molybdenum-tungsten alloy (MoW), etc.over the entire surface including the first common electrodes 124,followed by patterning.

At this time, the first common lines 125 are formed in parallel to thegate lines 112 while being brought into contact with the first commonelectrodes 124. The first common lines are extended to a region outsidean active region, and connected with an external driving circuit of theTFT array substrate.

Although the first common electrodes 124 are described above as beingformed before forming the gate lines 112, the present invention is notlimited to this process, and the first common electrodes 124 may beformed after forming the gate lines 112 or after forming data lines 115.

Next, after a gate insulation film 113 is formed by depositing aninorganic insulation material such as a silicon oxide (SiO.) or asilicon nitride (SiN.) over the entire surface including the gateelectrodes 112 a via plasma enhanced chemical vapor deposition (PECVD),amorphous silicon is deposited over the entire surface including thegate insulation film 113, followed by patterning via a photolithographyprocess to form a semiconductor layer 114 over the gate electrodes 112a.

Next, as shown in FIG. 8B, data lines 115 and source/drain electrodes115 a and 115 b are formed by depositing metal having a low resistance,such as copper (Cu), aluminum (AL), aluminum alloy (AlNd), molybdenum(Mo), molybdenum-tungsten alloy (MoW), etc. over the entire surfaceincluding the semiconductor layer 114, followed by patterning.

At this time, the data lines 115 cross with the gate lines 112 to defineRGBW sub-pixels, and the source/drain electrodes 115 a and 115 b areformed to overlap with both ends of the semiconductor layer 114, therebycompleting thin film transistors.

Then, a passivation layer 116 is formed by depositing an inorganicmaterial such as a silicon oxide, a silicon nitride and the like overthe entire surface including the data lines 115 or by applying anorganic material such as Benzocyclobutene (BCB), acryl resin and thelike thereto. Next, a contact hole 200 is formed by selectively removingthe passivation layer 116 such that the drain electrode of each thinfilm transistor is exposed.

Subsequently, as shown in FIG. 8C, pixel electrodes 117, each having aplurality of slits 160, are formed by depositing a transparentconductive material such as ITO or IZO over the entire surface includingthe passivation layer 116, followed by patterning. At this time, thepixel electrodes 117 formed in the respective sub-pixels are integrallyconnected with each other, and brought into contact with the drainelectrode 115 b via the contact hole 200 (see FIG. 8B).

Next, as shown in FIG. 80, black matrices 122, color filter layers 123,an overcoat layer 128, and second common electrodes 126 are formed on acolor filter array substrate 121 as follows. First, the black matrices122, are formed by depositing a material having a high reflectance suchas Cr on the color filter array substrate 121, and patterning thematerial so it remains at a site where light leakage occurs, forexample, at an edge of each sub-pixel and at a site of each thin filmtransistor.

Subsequently, a color resist containing pigments is applied to theentire surface including the black matrices 122, and patterned to formcolor filter layers 123. Typically, an R-color filter layer is formed inthe R sub-pixel through deposition and patterning of a red color resist,a G-color filter layer is formed in the G sub-pixel through depositionand patterning of a green color resist, and then a B-color filter layeris formed in the B sub-pixel through deposition and patterning of a bluecolor resist.

Next, the overcoat layer 128 is formed by flatly applying an organicmaterial such as acryl resin over the entire surface including theRGB-color filter layers 123. Since the overcoat layer 128 does notcontain pigment, it exhibits white color in the W sub-pixel. Although itis possible to form a separate W-color filter layer via application andpatterning of a white color resist during formation of the color filterlayers, the overcoat layer 128 formed in the W sub-pixel may be used inplace of the W-color filter layer.

Next, a transparent conductive material such as ITO or IZO is depositedover the entire surface including the overcoat layer 128, and patternedto form the second common electrode 126 only in each W sub-pixel. Thesecond common electrode 126 is provided for the purpose of controlling aviewing angle, and has the same size substantially as that of the Wsub-pixel.

Simultaneously, a second common line 127 (see FIG. 5) is formed tointegrally connect the second common electrodes 126 with each other.Here, the second common line 127 is extended to a region outside theactive region, and is electrically connected with an external drivingcircuit of the TFT array substrate via silver dots 191 (see FIG. 5),which are disposed at corners of a panel in a following process.

Finally, after applying a sealing material along an edge of the thinfilm transistor array substrate, and dispersing spacers on the activeregion, the color filter array substrate 121 is assembled to the TFTarray substrate 111 to face each other, and a liquid crystal layer 131is formed between these substrates, completing the LCD device accordingto the invention.

As apparent from the above description, the liquid crystal displaydevice and the method for manufacturing the same according to theinvention have advantageous effects as follows.

First, a white sub-pixel among RGBW-4 sub-pixels can be driven in thesame FFS mode as that of the adjacent RGB sub-pixels for a wide viewingangle mode, thereby widening the viewing angle while compensating whitebrightness, and is driven in an mode different from that of the adjacentRGB sub-pixels to form a vertical electric field for a narrow viewingangle mode, thereby lowering the viewing angle so as to protect privateinformation.

Secondly, according to the present invention, since the common electrodeis added only to an upper plate of each W sub-pixel, additionalmanufacturing costs are lowered, and the process is simple in comparisonto a related technique of controlling the viewing angle.

Additionally, the common electrode added to the upper plate is floatedor supplied with the same voltage as that of another common electrodeadded to a lower plate in the wide viewing angle mode, and is driven tohave a predetermined voltage difference between the upper and lowerplates in the narrow viewing angle mode, thereby allowing easy drivingof the LCD device.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A liquid crystal display device, comprising: gate lines and datalines crossing each other to define RGBW sub-pixels on a firstsubstrate; a thin film transistor formed at each crossing of the gateand data lines; a first common electrode formed in each region of theRGBW sub-pixels; a pixel electrode connected to the thin film transistorand insulated from the first common electrode, the pixel electrodehaving at least one slit; a second substrate attached to the firstsubstrate, wherein the first and second substrates face each other witha liquid crystal layer interposed therebetween; and a second commonelectrode on the second substrate and corresponding to each W sub-pixel.2. The LCD device according to claim 1, further comprising: RGB-colorfilter layers corresponding to the RGB sub-pixels on the secondsubstrate, respectively.
 3. The LCD device according to claim 2, furthercomprising: an overcoat layer on an overall surface of the secondsubstrate including the RGB-color filter layers between the secondcommon electrode and the RGB-color filter layers.
 4. The LCD deviceaccording to claim 1, wherein the W sub-pixel enables conversion inoperation between a wide viewing angle mode and a narrow viewing anglemode.
 5. The LCD device according to claim 4, wherein, in the wideviewing angle mode, a fringe field is created between the pixelelectrode and the first common electrode in the RGBW sub-pixels.
 6. TheLCD device according to claim 5, wherein the second common electrode isnot supplied with a voltage, or is supplied with a same voltage as thatapplied to the first common electrode.
 7. The LCD device according toclaim 4, wherein, in the wide viewing angle mode, the liquid crystallayer in the RGBW sub-pixels is driven in an FFS mode.
 8. The LCD deviceaccording to claim 4, wherein, in the narrow viewing angle mode, avertical electric field is formed between the first common electrode ofthe W sub-pixel and the second common electrode, and prevents light frompassing through the W sub-pixel.
 9. The LCD device according to claim 8,wherein, in the narrow viewing angle mode, a fringe field is createdbetween the pixel electrode and the first common electrode in the RGBsub-pixels.
 10. The LCD device according to claim 8, wherein the pixelelectrode of the W sub-pixel is supplied with a same voltage as thevoltage applied to the first common electrode, or supplied with avoltage less than a threshold voltage.
 11. The LCD device according toclaim 8, wherein the second common electrode of the W sub-pixel issupplied with a constant voltage to generate a voltage differencebetween the first common electrode and the second common electrode. 12.The LCD device according to claim 11, wherein the voltage differencebetween the first common electrode and the second common electrode ofthe W sub-pixel is about 1-4 V or about −4-−1 V so as to create avertical electric field therebetween.
 13. The LCD device according toclaim 11, wherein the voltage applied to the second common electrode isDC or AC voltage.
 14. The LCD device according to claim 4, wherein inthe narrow viewing angle mode, the liquid crystal layer in the RGBsub-pixels is driven in an FFS mode, and the liquid crystal layer in theW sub-pixel is tilted in a vertical direction.
 15. The LCD deviceaccording to claim 1, further comprising: an orientation film inside thefirst and second substrates; and upper and lower polarization plateattached to outer surfaces of the first and second substrates.
 16. TheLCD device according to claim 15, wherein the orientation film isorientated in a same direction as that of a polarization axis of one ofthe upper and lower polarization plates.
 17. The LCD device according toclaim 1, wherein the RGBW sub-pixels are disposed in a quad type or astripe type configuration.
 18. The LCD device according to claim 1,wherein the at least one slit of the pixel electrode is disposed in asame direction as that of the gate lines or the data lines.
 19. The LCDdevice according to claim 1, wherein the pixel electrode, the firstcommon electrode, and the second common electrode are transparentconductive layers.
 20. The LCD device according to claim 1, wherein thesecond common electrodes are connected to each other and supplied with avoltage from the first substrate via silver dots.
 21. A method formanufacturing a liquid crystal display device, comprising: forming firstcommon electrodes on a first substrate; forming gate lines and datalines to cross each other to define RGBW sub-pixels on the firstsubstrate; forming a thin film transistor at each crossing of the gateand data lines; forming a passivation layer on an overall surface of thefirst substrate including the thin film transistor; forming pixelelectrodes on the passivation layer, each pixel electrode having atleast one slit; attaching a second substrate to the first substrate,wherein the first and second substrate face each other, the secondsubstrate having a second common electrode formed to correspond only toeach W sub-pixel; and forming a liquid crystal layer between the firstand second substrates.
 22. The method according to claim 21, furthercomprising: forming black matrices on the second substrate; forming RGBWcolor filter layers above the black matrices corresponding to respectiveRGBW sub-pixels; and forming an overcoat layer on an overall surface ofthe second substrate including the color filter layers, before theforming the second common electrodes on the second substrate.
 23. Themethod according to claim 22, wherein each W color filter layer isformed at a same time with the forming of the overcoat layer.
 24. Themethod according to claim 23, wherein the W color filter layer and theovercoat layer are formed of a same material.
 25. The method accordingto claim 21, wherein the second common electrodes are formed of atransparent conductive layer.
 26. The method according to claim 25,wherein the second common electrodes are formed of either ITO or IZO.27. The method according to claim 21, wherein each of the second commonelectrodes has substantially a same size as that of the W sub-pixel. 28.The method according to claim 21, further comprising: forming a secondcommon line connecting the second common electrodes, at the forming ofthe second common electrodes wherein the second common line extends to aregion outside an active region.
 29. The method according to claim 28,further comprising: arranging the second common line to contact thesilver dots formed at corners of a panel to be electrically connectedwith a driving circuit of the first substrate.
 30. The method accordingto claim 21, further comprising: forming a first common line thatcontacts the first common electrodes at the forming of the gate lines.